1. Field of the Invention
The present invention relates to a compact rocker arm and fulcrum assembly for internal combustion engines having intake and/or exhaust poppet valves.
2. Background Art
Conventional internal combustion engines use a cams haft-driven valvetrain to operate intake and exhaust valves that control the exchange of gases in the combustion chambers formed between the engine block and cylinder head. Engines are often categorized by the location of the cams haft relative to the valves, with overhead cam valvetrains driven by a cams haft in the cylinder head over the valves, and pushrod valvetrains or “cam-in-block” valvetrains having the cams haft located in the engine block with the valves operated using pushrods and rocker arms.
Current four-valve-per-cylinder engines include two intake valves and two exhaust valves for each cylinder. As described in U.S. patent application Ser. No. 11/164,620 filed Nov. 30, 2005 and commonly owned by the assignee of the instant application, there are a number of advantages associated with having independent motion and lash adjustment for each valve rather than a bridged valvetrain implementation that actuates multiple valves in tandem. As such, a four-valve-per-cylinder application requires four independently pivotable rocker arms for each cylinder mounted in close proximity and properly aligned with the valve tips and pushrods (if present). Improper alignment may lead to uneven or side loading of the valves (and pushrods) with higher stresses resulting in higher rates of wear and potential noise, vibration, and harshness (NVH) concerns.
Relatively thin (or flat) rocker arms that pivot about a ball supported by a pedestal or fulcrum secured to the engine block have been developed as disclosed in U.S. Pat. Nos. 4,763,616 and 6,484,682, for example, and provide various advantages including reduced inertia relative to shaft-mounted rocker arms. Use of a ball/socket pivot arrangement requires that the rocker arm movement about two axes of rotation be limited or constrained so the rocker arm moves in a single plane about the third axis of rotation during operation. As such, these arrangements typically include one or more coplanar lateral or vertical surfaces on the pedestal or post to guide one side of each rocker arm so that it rotates or pivots in a single plane during operation to maintain desired alignment and loading. The pedestals or fulcrums also typically include one or more precision surfaces to provide for locating and aligning the rocker arms, valve tips, and pushrods relative to one another and the engine block, which increases cost and complexity of the assembly.